1. Field of the Invention
The invention relates to a method of testing a power module and more particularly to a test method for verifying the correct status of the insulation of a power module. The invention applies in particular to testing power modules for onboard power converters on rail vehicles. The invention also concerns a device for implementing the test method according to the invention.
2. Description of the Prior Art
International Electrotechnical Commission (IEC) Standard 1287-1 discloses a method of testing onboard power converters on rail vehicles whose object is to verify the correct status of the insulation of a completely assembled converter. In that method, the main terminals of the converter and the collectors, emitters and gates controlling all the semiconductor components are connected together. The level of partial discharges is then measured when an alternating current voltage or a direct current voltage is applied between the interconnected terminals and the metal baseplate supporting the dielectric substrate supporting the components of the power module.
This kind of test method has the drawback that it tests only the insulation associated the substrate, which represents only a portion of the dielectric stack used in the power module, the insulation associated with the encapsulation of the components, for example, not being tested.
Also, one object of the present invention is therefore to propose a simple and economical method of testing a power module able to detect partial discharge problems in the dielectric gel covering the power components, between the power terminals, or at the interface between the various dielectric materials.
To this end, the invention provides a method of testing a power module including a control gate, an emitter, a collector, at least one power component on a dielectric substrate and a diode connected in antiparallel with the power component, which method measures partial discharges occurring between the emitter and the collector when an alternating current voltage source superimposed on a direct current voltage source is connected between the collector and the emitter of the power module, the voltage Vtest received by the power module between the collector and the emitter verifies at all times the condition Vtest greater than 0 so that the diode never conducts, and the power component is maintained in a turned off state during the test by means of a direct current voltage source connected between the control gate and the emitter.
According to another feature of the invention a power module includes a plurality of emitters, a plurality of collectors, a common control gate, a plurality of power components connected in parallel, and a diode connected in antiparallel with each power component, which method measures partial discharges occurring between the emitters, which are electrically connected to each other, and the collectors, which are electrically connected to each other, when an alternating current voltage source superposed on a direct current voltage source is connected between the emitters and the collectors of the power module, the voltage Vtest received by the power module between the collectors and the emitters verifies at all times the condition Vtest greater than 0 so that the diodes never conduct, and the power modules are maintained during the test in the turned off state by means of a direct current voltage source connected between the common control gate and the emitters.
According to another feature of the invention the power components are Insulated Gate Bipolar Transistors (IGBT).
The invention also provides a device for testing a power module for implementing the method previously described and which includes two terminals adapted to be connected to an alternating current voltage source superposed on a direct current voltage source and means for measuring partial discharges between the two terminals, and in which the voltage Vtest between the terminals verifies at all times the condition Vtest greater than 0.
According to another feature of the invention the two terminals are adapted to be connected to a direct current voltage generator in series with an alternating current voltage generator.
According to another feature of the invention the two terminals are adapted to be connected to a direct current voltage generator in parallel with an alternating current voltage generator.
According to another feature of the invention the power supply terminal are respectively connected to a first circuit for connecting together the various collectors of the power module and a second circuit for connecting together the various emitters of the power module.
The aims, aspects and advantages of the present invention will become clearer from the following description of one particular embodiment of the invention, which description is given by way of non-limiting example only and with reference to the accompanying drawings.